1、Particle contamination in oil is specified from particle count. Two basic standards the ISO and NAS systems are com-monly used as contamination reference. The two cleanliness standards can not be directly compared or converted, as the basic principles within the two systems differ to much. This is e
2、xplained in the next pages. However, the following tables gives some rough guidelines of common practice for setting targets of cleanliness levels in different systems. As seen both ISO 4406 and NAS 1638 are represented. These guidelines are minimum fluid cleanliness levels required for an acceptabl
3、e lifetime of equipment and components. Many factors influence lifetime and demands to fluid quality. High reliability systems enhance demands to quality, and high pressure systems and heavy bearing load increase de-mands. The last three columns of the tables indicate the range of the GreenOil filte
4、r system. Although the filters may be put into service in many application, parameters as fluid volume and viscosity should be taken into consideration before expecta-tions to contamination limits are set. Working with ISO4406 and NAS 1638 GreenOil Standard Date: 15-12-2005 Technical Paper 004 Parti
5、cle Contamination ISO4406 and NAS1638 Page 1 af 3 Saved as: Technical Paper 004 Hydraulic Equipment and Components Pressure Range GreenOil Filter Inserts ISO 4406 NAS 1638 H T M Silt sensitive, aerospace, robots, High pressure 250-400 bar 14/12/9 4 ISO 10/6 NAS 3 Servo systems, injection moulding, H
6、igh pressure 250-400 bar 16/14/11 5 Proportional and flow valves, High pressure 250-400 bar 17/15/12 6 Piston pumps and motors, Normal pressure 150-250 bar 18/16/13 7 Typical new hydraulic oil 18/16/13 7 Gear pump and motors, Medium pressure 50-150 bar 19/17/14 8 Cylinders and Flow Control Low press
7、ure 0-50 bar 20/18/15 9 Lubrication Oil Equipment and Components Ball bearings, turbine oils, Small and medium gearboxes 14/12/9 4 Roller bearings Transmission gearboxes 16/14/11 5 ISO 14/11 NAS 5 Journal bearings Industrial gearboxes 17/15/12 6 Mobile equipment and gearboxes Paper mill 18/16/13 7 I
8、SO 16/12 NAS 7 Diesel engine lubrication 19/17/14 8 Heavy duty gearboxes 20/18/15 9 Typical new lubrication oil 20/18/15 9 Typical in-line filtration 21/19/15 10 Minimum Class Requirement Page 2 Technical Paper 004 Introduction Contamination in oil is specified from particle count. Two basic methods
9、 are used: Laser based particle count analysis equipment gives directly information on particle sizes (micron= u) and figures within specified size ranges. The other method utilize filtering an oil sample through an very fine mesh filter paper. The particles on the surface of the filter paper is the
10、n monitored in a microscope and com-pared to standard contamination pictures to indicate the de-gree of contamination. Contamination classes Instead of specifying particle counts contamination is sepa-rated into classes defined in two major systems ISO (International Standard Organisation) and NAS (
11、National Air-space Standard). Each class defines a range of counts within an exponential scale. Unfortunately, the two systems are not identical and can not be converted in simple mathematics. However, some simple guidelines can be given. First of all lets look at the two sys-tems. NAS1638 The NAS s
12、ystem divides particles in 5 ranges. Furthermore, the NAS system specify different counts within each particle range to score a specific class. In practice oil samples will show up to gain almost same NAS class rating within the different particle ranges. The system is designed to match the most com
13、mon found con-tamination which has really many small particles and fever big particles. The sidebar example shows a typical oil analy-sis with counts divided in the 5 classes. As seen the classes ranges from 3 to 6, however, the resulting NAS class is de-fined as the particle count with the highest
14、(worse) score, and only this class is specified. The sidebar example will be classified as “NAS1638 class 6”. Classes 5 to 15 15 to 25 25 to 50 50 to 100 100 00 125 22 4 1 0 0 250 44 8 2 0 1 500 89 16 3 1 2 1,000 178 32 6 1 3 2,000 356 63 11 2 4 4,000 712 126 22 4 5 8,000 1,425 253 45 8 6 16,000 2,8
15、50 506 90 16 7 32,000 5,700 1,012 180 32 8 64,000 11,400 2,025 360 64 9 128,000 22,800 4,050 720 128 10 256,000 45,600 8,100 1,440 256 11 512,000 91,200 16,200 2,880 512 12 1,024,000 182,400 32,400 5,760 1024 Particle Classes Size Range per 100 ml NAS 1638 Particle range Counts Class 5-15 u 8450 6 1
16、5-25 u 11982 5 25-50 u 312 6 50-100 u 46 6 100 u 2 3 Resulting class 6 NAS analysis example ISO 4406 The ISO system is not as practical orientated as the NAS sys-tem. First of all it consists of 2 or 3 figures. Each figure de-fine a class within a size range. A typical ISO 4406 oil test will be indi
17、cated as: 17/15/12 Particles 2 u Particles 5 u Particles 15 u As seen particles less than 2 u are omitted. The original ISO4406 operated with only two digits omitting counts below 5 u. This standard is still widely accepted, though it does not relieve the same information as the newer 3 digit ISO ve
18、rsion. 15/12 Particles 5 u Particles 15 u The cleanliness levels represent the particle counts as shown in the table. (Not to get stuck in mathematics: the class represents powers of the numeral 2. A cleanliness level 15 indicates counts be-tween 214(16,383) and 215(32,768) for a sample of 100 ml fl
19、uid). The sidebar example will be classified “ISO4406 17/15/12” NAS and ISO To conclude: NAS and ISO can not be compared directly. As seen both NAS and ISO operates exponentially. In both systems, the particle counts must be halved to reduce the class or cleanliness level one digit. In practice the
20、great advantage of the NAS system is that con-tamination is identified by only one class number. For identi-fying contamination sources this could be a limitation which does not apply as much for the ISO system which is more open yet complicated. The NAS and ISO 2-digit systems does not take particl
21、es less than 5 u into consideration. The ISO 3-digit system monitors down to 2 u particles. The ISO system has the same class definition throughout the particle ranges. The NAS system has different definition of class within each particle range. Page 3 Technical Paper 004 Class Number More Than Up t
22、o and Including 24 8,000,000 1,600,000 23 4,000,000 8,000,000 22 2,000,000 4,000,000 21 1,000,000 2,000,000 20 500,000 1,000,000 19 250,000 500,000 18 130,000 250,000 17 64,000 130,000 16 32,000 64,000 15 16,000 32,000 14 8,000 16,000 13 4,000 8,000 12 2,000 4,000 11 1,000 2,000 10 500 1,000 9 250 500 8 130 250 7 64 130 6 32 64 5 16 32 4 8 16 3 4 8 2 2 4 1 1 2 0 0.5 1 00 0.25 0.5 Number of particles per 100 ml ISO 4406 ISO analysis example: 17/15/12 Particle range Counts Class 100 u 3 12
